how do i set up apple tv 3rd generation with a new remote

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i connected everything put the hdmi at the back of the unit and into back of tv
the apple tv is flashing but doesnt sync with the tv
it used to but i lost my remote got a new one and im trying to make it work again , tried to push appropriate buttons on the remote to have apple tv unit and tv recognize it but doesnt work so far
who can i talk to - Help!!!
carl